1. Field of the Invention
This invention relates to a novel ester compound exhibiting liquid crystal phases within a broad temperature range and to a liquid crystal composition containing the same as an active ingredient.
2. Description of the Prior Art
Display elements utilizing liquid crystals have been broadly used for watches, electric calculators, etc. These liquid crystal display elements utilize the optical anisotropy and the dielectric anisotropy of liquid crystal substances. Liquid crystal phases include nematic liquid crystal phase, smectic liquid crystal phase, and cholesteric liquid crystal phase, and among these phases, display elements utilizing nematic liquid crystal phase have most broadly been practically used. These display elements are classified into the following types corresponding to the electrooptical effect applied to liquid crystal display elements: TN (twisted nematic) type, DS (dynamic scattering) type, guest-host type, DAP type, etc., and those which exhibit liquid crystal phases within as broad a temperature range as possible in the natural world are preferred.
At present, however, there is no single liquid crystal substance which satisfies such conditions, and mixtures of several kinds of liquid crystal substances or mixtures of the above ones with non-liquid crystalline substances have been practically used. Further, these substances have been required to be stable to moisture, light, heat, air, etc.
Still further, it has been required for the above mixtures of liquid crystal substances and the like, that is, liquid crystal compositions, that the threshold voltage and the saturation voltage for driving the compositions be as low as possible, and also the viscosity of the compositions be as low as possible in order to raise the response speed. Thus, compounds which are preferred as a component constituting the liquid crystal compositions suitable to the above object have been required. Furthermore, it has been required for the above liquid crystal compositions that the upper limit of their use temperature range, i.e., the nematic temperature range, be as high as possible, and compounds which, when added as a constituting component to the liquid crystal compounds, raise the nematic phase-isotropic liquid phase transition point (hereinafter abbreviated to N-I point) thereof without increasing their viscosity have been required.
As such compounds satisfying the above requirements, the present inventors have previously invented compounds expressed by the following formulas (II) and (III) (Japanese patent application No. Sho 57-36808/1982; Japanese patent application laid-open No. Sho 59-1447/1984), and further, compounds expressed by the following formulas (IV) and (V) (Japanese patent application No. Sho. 57-72237; Japanese patent application laid-open No. Sho 58-188841/1983) and (Japanese patent application No. Sho 57-93743/1982; Japanese patent application laid-open No. Sho 58-210047/1983): ##STR3##
In the above formulas (II)-(V), R represents an alkyl group of 1 to 10 carbon atoms.
Further, the present inventors have invented compounds expressed by the following formulas (VI), (VII), (VIII) and (IX), as substances which are preferred for raising the upper limit of nematic temperature range among the above-mentioned objects (Japanese patent application No. Sho 57-146595/1982; Japanese patent application laid-open No. Sho 59-36643/1984), (Japanese patent application No. Sho 57-153601/1982; Japanese patent application laid-open No. Sho 59-42344/1984), (Japanese patent application No. Sho 58-3254/1983; Japanese patent application laid-open No. Sho 59-128356/1984) and (Japanese patent application No. Sho 58-11906/1983; Japanese patent application laid-open No. Sho 59-137447/1984): ##STR4##
In the above formulas (VI), (VII), (VIII) and (IX), R represents a hydrogen atom or an alkyl group of 1 to 10 carbon atoms.
However, it goes without saying that liquid crystal compositions which are superior to those using the above compounds have been required.